Method of making a CMOS semiconductor device using a stressed silicon-on-insulator (SOI) wafer

ABSTRACT

A method for forming a complementary metal oxide semiconductor (CMOS) semiconductor device includes providing a stressed silicon-on-insulator (sSOI) wafer comprising a stressed semiconductor layer having first and second laterally adjacent stressed semiconductor portions. The first stressed semiconductor portion defines a first active region. The second stressed semiconductor portion is replaced with an unstressed semiconductor portion. The unstressed semiconductor portion includes a first semiconductor material. The method further includes driving a second semiconductor material into the first semiconductor material of the unstressed semiconductor portion defining a second active region.

FIELD OF THE INVENTION

The present invention relates to the field of electronic devices, andmore particularly, to a method of making semiconductor devices.

BACKGROUND OF THE INVENTION

Some semiconductor devices utilize semiconductor-on-insulator (SOI)technology, in which a thin layer of a semiconductor, such as silicon,is separated from a semiconductor substrate by a relatively thickelectrically insulating layer. This thick electrically insulating layeris also referred to as a buried oxide (BOX) layer. The semiconductorlayer typically has a thickness of a few nanometers, whereas thesemiconductor substrate typically has a thickness of a few tens ofnanometers.

SOI technology offer certain advantages compared to traditional bulktechnology for Complementary Metal Oxide Semiconductor (CMOS) devices.CMOS devices include nMOSFET transistors and pMOSFET transistors bothformed in the thin silicon layer which overlies the buried oxide (BOX)layer. SOI technology allows CMOS devices to operate at lower powerconsumption while providing the same performance level.

One particular type of SOI technology that is helping to allow forcontinued CMOS scaling is fully depleted SOI (FDSOI). As opposed to apartially depleted SOI (PDSOI) device, in an FDSOI device a relativelythin semiconductor channel layer is provided over the buried oxide (BOX)layer, such that the depletion region of the device covers the wholelayer. FDSOI devices may provide advantages such as higher switchingspeeds and a reduction in threshold voltage roll off, as compared toPDSOI devices, for example.

To improve CMOS device performance, stress may be introduced into thechannels of the field effect transistors (FETs). When applied in alongitudinal direction (i.e., in the direction of current flow), tensilestress is known to enhance electron mobility (i.e., n-channel MOSFETdrive currents) while compressive stress is known to enhance holemobility (i.e., p-channel MOSFET drive currents).

Consequently, tensile strained silicon-on-insulator (sSOI) is a mainperformance driver for nMOSFET transistors, and compressive strainedsilicon-germanium-on-insulator (SGOI) is a main performance driver forpMOSFET transistors.

To form an SGOI pMOSFET transistor on an sSOI substrate or wafer isdifficult. Growing SiGe on an sSOI wafer often times leads to a roughsurface resulting in mobility loss. In addition, a high germaniumcontent in the silicon-germanium is needed to compensate for tensilestrain. Otherwise, this leads to a high density of interface trap (DIT)value, where the DIT designates a density of traps at an interfacebetween two layers.

One approach for forming a stressed Si/SiGe dual channel device isdisclosed in U.S. published patent application no. 2013/0029478. Anepitaxial SiGe layer is formed on an SOI substrate, and an Si cap layeris formed on the SiGe layer. A photoresist layer is formed on the Si caplayer, and part of the Si cap layer is removed. A Si layer isepitaxially grown on the exposed SiGe layer. An ion implantation isperformed to distribute implanted ions within the silicon cap layer.Annealing is performed to relax the stress in part of the SiGe layer andtransfer stress to the epitaxial Si material thereon to form strainedsilicon. The formed strained silicon is used to form an nMOSFETtransistor channel and the region of the SiGe layer covered byphotoresist is used to form a pMOSFET transistor channel.

Despite the existence of such configurations, further enhancements inSOI devices may be desirable in some applications, particularly when theSOI wafer is a stressed SOI wafer.

SUMMARY OF THE INVENTION

A method for forming a complementary metal oxide semiconductor (CMOS)semiconductor device comprises providing a stressed silicon-on-insulator(sSOI) wafer comprising a stressed semiconductor layer having first andsecond laterally adjacent stressed semiconductor portions, with thefirst stressed semiconductor portion defining a first active region. Themethod may further comprise replacing the second stressed semiconductorportion with an unstressed semiconductor portion, with the unstressedsemiconductor portion comprising a first semiconductor material. Asecond semiconductor material may be driven into the first semiconductormaterial of the unstressed semiconductor portion to define a secondactive region.

The first semiconductor material may comprise silicon, and the secondsemiconductor material may comprise silicon and germanium. The secondactive region is advantageously formed in a relatively straightforwardmanner without the need for complex steps.

A mask layer may be formed over the first stressed semiconductor portionbefore replacing the second stressed semiconductor portion with theunstressed semiconductor portion.

Replacing the second stressed semiconductor portion with the unstressedsemiconductor portion may comprises removing the second stressedsemiconductor portion except for a second stressed semiconductor portionbottom layer, and forming the unstressed semiconductor portion on thesecond stressed semiconductor portion bottom layer. The second stressedsemiconductor portion bottom layer may be annealed before forming theunstressed semiconductor portion. In addition, the unstressedsemiconductor portion may also be annealed.

Driving the second semiconductor material into the first semiconductormaterial may comprise forming a second semiconductor layer comprisingthe second semiconductor material over the unstressed semiconductorportion, and oxidizing the second semiconductor layer to drive thesecond semiconductor material into the first semiconductor material.

The method may further comprise forming first and second gate stacksover the first and second active regions, respectively. First raisedsource and drain regions defining a first channel therebetween may beformed in the first active region under the first gate stack. Secondraised source and drain regions defining a second channel therebetweenmay be formed in the second active region under the second gate stack.

The stressed SOI wafer may comprises a fully depleted SOI (FDSOI) wafer.The first active region may be for an n-channel metal-oxidesemiconductor field-effect transistor, and the second active region maybe for a p-channel metal-oxide semiconductor field-effect transistor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top-level flowchart illustrating a method for forming acomplementary metal oxide semiconductor (CMOS) semiconductor device inaccordance with the present embodiment.

FIG. 2 is a more detailed flowchart illustrating the method of FIG. 1.

FIGS. 3-9 are a series of cross-sectional diagrams illustrating themethod of FIG. 2.

FIG. 10 is a cross-sectional diagram of the CMOS semiconductor deviceformed by the method of FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present embodiments will now be described more fully hereinafterwith reference to the accompanying drawings, in which preferredembodiments are shown. The embodiments may, however, be embodied in manydifferent forms and should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the disclosure to those skilled in the art. Likenumbers refer to like elements throughout.

Referring initially to the flowchart 20 in FIG. 1, a method for forminga complementary metal oxide semiconductor (CMOS) semiconductor deviceincludes, from the start (Block 21), providing a stressedsilicon-on-insulator (sSOI) wafer at Block 22 comprising a stressedsemiconductor layer having first and second laterally adjacent stressedsemiconductor portions, with the first stressed semiconductor portiondefining a first active region. The method further comprises replacingthe second stressed semiconductor portion at Block 23 with an unstressedsemiconductor portion, with the unstressed semiconductor portioncomprising a first semiconductor material. A second semiconductormaterial may be driven into the first semiconductor material of theunstressed semiconductor portion at Block 24 to define a second activeregion. The method ends at Block 25.

The first semiconductor material may comprise silicon, and the secondsemiconductor material may comprise silicon and germanium. The secondactive region is advantageously formed in a relatively straightforwardmanner without the need for complex steps.

As will be discussed in greater detail below, asilicon-germanium-on-insulator (SGOI) p-channel metal-oxidesemiconductor field-effect (pMOSFET) transistor is formed on a stressedsilicon-on-insulator (sSOI) wafer. The stressed silicon on the sSOIcorresponding to the pMOSFET is intentionally thinned, and asilicon-germanium layer is formed on the thinned stressed silicon. Ann-channel metal-oxide semiconductor field-effect (nMOSFET) transistor isformed in the stressed silicon-on-insulator (sSOI) wafer.

A more detailed method for forming the CMOS semiconductor device 45 willnow be discussed in reference to the flowchart 30 in FIG. 2 and to theprocess flow illustrated in FIGS. 3-8. From the start (Block 31), themethod includes providing at Block 32 a stressed silicon-on-insulator(SOI) wafer 50 comprising a stressed semiconductor layer 56 having firstand second laterally adjacent stressed semiconductor portions 70 and 80,as illustrated in FIG. 3. The first stressed semiconductor portion 70defines a first active region 72.

The sSOI wafer 50 includes a semiconductor substrate or wafer 52, aburied oxide (BOX) layer 54 on the semiconductor substrate, and thestressed semiconductor layer 56 on the buried oxide layer. In oneembodiment, the semiconductor substrate 52 comprises silicon, and thestressed semiconductor layer 56 also comprises silicon.

The sSOI wafer 50 may be a fully depleted SOI (FDSOI) wafer, as readilyappreciated by those skilled in the art. In addition, the SOI wafer 50may be an ultra-thin body and box (UTBB) wafer, as also readilyappreciated by those skilled in the art. In one embodiment, a thicknessof the semiconductor substrate 52 may be within a range of about 10 to25 nm, and a thickness of the stressed semiconductor layer 56 may bewithin a range of about 7 to 10 nm, for example.

A mask layer 90 is formed over the first stressed semiconductor portion70 at Block 34 and as illustrated in FIG. 4. The mask layer 90 protectsthe first stressed semiconductor portion 70 while a second active regionis defined. The second active region is defined in the areacorresponding to the second stressed semiconductor portion 80, which islaterally adjacent the first active region 72.

The second stressed semiconductor portion 80 is replaced with anunstressed semiconductor portion 100, as illustrated in FIG. 6. Theunstressed semiconductor portion 100 includes a first semiconductormaterial. More particularly, replacing the second stressed semiconductorportion 80 with the unstressed semiconductor portion 100 includesremoving the second stressed semiconductor portion 80 at Block 36 exceptfor a second stressed semiconductor portion bottom layer 81, asillustrated in FIG. 5.

The second stressed semiconductor portion 80 may be thinned based on anSC1 wet etch, for example. Alternatively, oxidation may be used to thinthe second stressed semiconductor portion 80. With oxidation, a thinoxide layer is deposited and then oxidation occurs. Both the SC1 wetetch and the oxidation can be well controlled so that a thickness of thesecond stressed semiconductor portion bottom layer 81 may be within arange of about 2 to 3 nm, as readily appreciated by those skilled in theart.

To relax the second stressed semiconductor portion bottom layer 81, ahigh temperature anneal may be performed at Block 38. After theannealing, the unstressed semiconductor portion 100 is formed at Block40 on the second stressed semiconductor portion bottom layer 81 and asillustrated in FIG. 6. The first semiconductor material making up theunstressed semiconductor portion 100 may be epitaxially grown, asreadily appreciated by those skilled in the art. A thickness of theunstressed semiconductor portion 100 may be within a range of about 5 to7 nm, for example. The first semiconductor material comprises silicon,for example, and is intrinsic, i.e., undoped. Intrinsic silicon helps toensure that a top surface of the unstressed semiconductor portion 100 isunstressed.

Trench isolation regions 180 are formed to bound the first active region72 and the adjacent unstressed semiconductor portion 100, as illustratedin FIG. 7. Optionally, a chemical-mechanical polishing may be performedbefore the trench isolation regions 180.

To further relax the second stressed semiconductor portion bottom layer81, another high temperature anneal may be performed at Block 42 afterforming the unstressed semiconductor portion 100. Referring now to FIG.8, a second semiconductor material is driven into the firstsemiconductor material of the unstressed semiconductor portion 100defining the second active region 82.

More particularly, driving the second semiconductor material into thefirst semiconductor material includes forming a second semiconductorlayer 110 and comprising the second semiconductor material over theunstressed semiconductor portion 100 at Block 43. In this example, thesecond semiconductor material comprises silicon and germanium. Thesilicon and germanium forming the second semiconductor layer 110 isepitaxially grown on the unstressed semiconductor portion 100. Athickness of the second semiconductor layer 110 may be within a range ofabout 5 to 7 nm, for example. Driving the second semiconductor material(i.e., silicon and germanium) into the first semiconductor material(i.e., silicon) is based on oxidizing the second semiconductor layer 110at Block 44. This forms a new second stressed semiconductor portion 112.

Referring now to FIG. 9, the hard mask 90 is removed and the stressedsilicon-on-insulator (SOI) wafer 50 includes the first stressedsemiconductor portion 70 defining the first active region 72, and thenew second stressed semiconductor portion 112 defining the second activeregion 82. The new second stressed semiconductor portion 112 definingthe second active region 82 is advantageously formed in a relativelystraightforward manner without the need for complex steps.

The method further comprises forming first and second gate stacks 120,130 over the first and second active regions 72, 82, respectively, atBlock 46. In the illustrated embodiment of the CMOS semiconductor device45 shown in FIG. 10, the first gate stack 120 includes a gate dielectriclayer 122, a gate electrode layer 124, and sidewall spacers 126.Similarly, the second gate stack 130 includes a gate dielectric layer132, a gate electrode layer 134, and sidewall spacers 136.

First raised source and drain regions 140, 142 are formed at Block 47 todefine a first channel 144 therebetween in the first active region 72under the first gate stack 120. Similarly, second raised source anddrain regions 150, 152 are formed at Block 48 to define a second channel154 therebetween in the second active region 82 under the second gatestack 130.

The first channel region 144 is for an n-channel metal-oxidesemiconductor field-effect transistor (nMOSFET) 160, and the secondchannel region 154 is for a p-channel metal-oxide semiconductorfield-effect transistor (pMOSFET) 170. The nMOSFET 160 and the pMOSFET170 are separated by a shallow trench isolation (STI) region 180. Themethod ends at Block 49.

In view of the above, a variety of different transistor structures maybe implemented, including but not necessarily limited to: planar CMOS,high-k metal gate CMOS, PD-SOI, FD-SOI, UTBB, vertical double gate,buried gate, FinFET, tri-gate, multi-gate, 2D, 3D, raised source/drain,strained source/drain, strained channel, and combinations/hybridsthereof, for example.

Many modifications and other embodiments will come to the mind of oneskilled in the art having the benefit of the teachings presented in theforegoing descriptions and the associated drawings. Therefore, it isunderstood that the invention is not to be limited to the specificembodiments disclosed, and that modifications and embodiments areintended to be included within the scope of the appended claims.

The invention claimed is:
 1. An electronic device, comprising: astressed silicon-on-insulator (SOI) substrate including a substrate, aninsulating layer on the substrate, and a stressed semiconductor layer onthe insulating layer, the stressed semiconductor layer having: first andsecond laterally adjacent stressed semiconductor portions, the firststressed semiconductor portion including silicon and defining a firstactive region, and the second stressed semiconductor portion including astressed silicon bottom layer and a stressed silicon-germanium top layeron the stressed silicon bottom layer defining a second active region,the stressed silicon bottom layer and the stressed silicon-germanium toplayer having substantially the same width; a first trench isolationregion separating the first and second laterally adjacent stressedsemiconductor portions and extending through the insulating layer andinto the substrate; and a second trench isolation region extendingthrough the insulating layer and into the substrate, the stressedsilicon bottom layer and the stressed silicon-germanium top layerextending between the first trench isolation region and the secondtrench isolation region.
 2. The electronic device according to claim 1,further comprising: first and second gate stacks over the first andsecond active regions, respectively; first raised source and drainregions defining a first channel in the first active region under thefirst gate stack; and second raised source and drain regions defining asecond channel in the second active region under the second gate stack.3. The electronic device according to claim 2 wherein the first channelis for an n-channel metal-oxide semiconductor field-effect transistor(nMOSFET) having a FinFET structure, and the second channel is for ap-channel metal-oxide semiconductor field-effect transistor (pMOSFET)having a FinFET structure.
 4. The electronic device according to claim 1wherein the stressed SOI substrate comprises a fully depleted SOI(FDSOI) wafer.
 5. A device, comprising: a substrate having a surface; afirst semiconductor layer on the surface of the substrate, the firstsemiconductor layer having a first stressed portion and a second relaxedportion that is thinner than the first stressed portion; and a secondstressed semiconductor layer on the second relaxed portion of the firstsemiconductor layer and adjacent to the first stressed portion of thefirst semiconductor layer, the second stressed semiconductor layer beinga different combination of materials than the first semiconductor layer,a surface of the first semiconductor layer being coplanar with a surfaceof the second stressed semiconductor layer.
 6. The device of claim 5,further comprising an isolation region in the substrate and between thefirst stressed portion of the first semiconductor layer and the secondstressed semiconductor layer.
 7. The device of claim 6, furthercomprising: a first gate on the first stressed portion of the firstsemiconductor layer; and a second gate on the second stressedsemiconductor layer.
 8. The device of claim 7, further comprising asource and drain formed in the first stressed portion of the firstsemiconductor layer and a source and drain formed in the second stressedsemiconductor layer.
 9. The device of claim 8, further comprising afirst channel between the source and drain adjacent to the first gate inthe first stressed portion of the first semiconductor layer and a secondchannel between the source and drain adjacent to the second gate in thesecond stressed semiconductor layer.
 10. The device of claim 5, furthercomprising an nMOSFET formed in and on the first stressed portion of thefirst semiconductor layer and a pMOSFET formed in and on the secondstressed semiconductor layer.
 11. The device of claim 5 wherein thesecond stressed semiconductor layer includes silicon germanium.
 12. Adevice, comprising: a substrate; an insulating region formed in thesubstrate; a first semiconductor layer on the substrate, the firstsemiconductor layer having a first stressed semiconductor portion, asecond relaxed semiconductor portion, and a third stressed semiconductorportion that is between the substrate and the second relaxedsemiconductor portion, the second relaxed semiconductor portion and thethird stressed semiconductor portion being separated from the firststressed semiconductor portion by the insulating region; a secondstressed semiconductor layer on the second relaxed semiconductorportion, the first stressed semiconductor portion being separated fromthe second stressed semiconductor layer by the insulating region, thefirst stressed semiconductor portion being a different combination ofmaterials than the second stressed semiconductor layer; a firsttransistor formed on the first stressed semiconductor portion; and asecond transistor formed on the second stressed semiconductor layer. 13.The device of claim 12 wherein the first transistor includes a sourceand drain formed in the first stressed semiconductor portion and thesecond transistor includes a source and drain formed in the secondstressed semiconductor layer.
 14. The device of claim 13 wherein thefirst transistor includes a first channel between the source and drainin the first stressed semiconductor portion and the second transistorincludes a second channel between the source and drain in the secondstressed semiconductor layer.
 15. The device of claim 12 wherein thesecond stressed semiconductor layer includes silicon germanium.